MONACO (AP) Rafael Nadal is wary of saying he's fully recovered from a troublesome right thigh injury as he defends his Monte Carlo Masters title.

The top-ranked Spaniard only recently returned to action at the Davis Cup, after a recurrence of the injury forced him out of the Mexico Open and then Masters tournaments at Indian Wells and Miami last month.

Those setbacks followed his crushing disappointment at the Australian Open, where he was forced to retire in the fifth set of the quarterfinal against Marin Cilic.

Nadal had expected to make his comeback in Acapulco, but the injury flared up again during a last practice session with French player Adrian Mannarino. Looking back on it Sunday, the 16-time Grand Slam champion said it was mentally "even harder than what happened in Australia" because he was so convinced he would play.

"I did all the things the right way, practicing one week before, to be ready for the tournament and then it happened," Nadal told reporters. "You're in Acapulco, you fly all the way ... Then the doctors told me: `You will not be able to play in Indian Wells, Miami.' So that was hard to accept."

So was the painstakingly dull recovery which followed.

"I was unable to do any physical work because the psoas (muscle) was affecting all the movements I could do," he said. "It was a boring time because I don't like to be doing nothing."

Nadal wasn't bored last weekend, however, winning both his Davis Cup singles against Germany without dropping a set. Although he appears to have slotted straight back into his clay groove, his Acapulco setback leaves him circumspect about speaking too soon.

"Well it happened twice, so you never know," he said. "Of course it stays a little bit in your mind."

Nadal begins his bid for a record-extending 11th Monte Carlo title with a second-round match against either Aljaz Bedene or Mirza Basic. He needs to win the tournament or Roger Federer will reclaim top ranking in their seemingly endless fight for supremacy. They have won the last five Grand Slams, three for Federer

But with 20-time major winner Federer again skipping the clay season, Nadal must wait a while longer to try and avenge a run of five straight defeats to the Swiss star.

He took a swipe, although an amiable one, at Federer.

"He says he will love to play against me again in best of five sets on clay, and I thought he would play Roland Garros," Nadal said, with a wry smile. "A few days later he says he will not play in one (clay) event, so there's a little bit of controversy with that."

Nadal's victory at Monte Carlo last year made him the first men's tennis player in the Open era to win the same title 10 times. He then won a 10th French Open.

He feels at home at the picture-postcard tournament with its center court perched over the glittering Mediterranean sea. The Monte Carlo tournament launched his career as a scraggly-haired 16-year-old in 2003, although the sun had long set when he beat defending French Open champion Albert Costa under floodlights in the second round.

"I always feel good when I am here," Nadal said. "It's been a love story."

The only Monte Carlo final that the 31-year-old Nadal has lost was to Novak Djokovic in 2013. Djokovic added another Monte Carlo title in 2015, during his pomp.

But the former top-ranked Serb looks a shadow of the player he was. Hindered by a persistent right elbow injury, his ranking has tumbled to 13.

Earlier this month, Djokovic stopped working with Andre Agassi and Radek Stepanek - the latest in a series of coaching changes for the 12-time major champion.

After significant rest during the second half of last year and a medical procedure in February, Djokovic spoke confidently of being pain-free - at long last.

Then, he lost his first match at the Miami Open in straight sets.

Djokovic used to be the player everyone was chasing. He even beat Nadal during a glorious run of seven straight finals and holds a 26-24 winning record against him.

They have won a record 30 Masters each, but Nadal looks the more likely to get No. 31.